This invention relates to controls for continuously variable pulley systems and more particularly the squeeze controls for such systems.
Prior art directs squeeze controls for continuously variable transmissions, of the pulley and belt type, are generally of the mechanical type. These devices employ a pair of relatively movable cam members which are disposed in the input or output torque path. The transmitted torque causes axial movement of one of the cam members which in turn causes a squeeze load to be imposed on the pulley system.
These systems are effective; however, they do require additional axial space which increases the overall length of the continuously variable transmission. The mechanical systems are quite often accompanied by a hydraulic system which is used to supplement the squeeze force and to establish the overall ratio within the continuously variable transmission. The hydraulic systems generally depend on external signals, such as engine throttle position or engine vacuum, to determine the torque level and therefore the squeeze force required.
A hydromechanical system, such as that shown in U.S. Pat. No. 4,608,031 issued Aug. 26, 1986, describes the continuously variable transmission wherein a planetary gear mechanism on the output shaft is subjected to output torque. One of the gear elements, the carrier, is connected to a servo valve element which in turn is operable to distribute fluid to a control piston on one of the pulleys for squeeze control and ratio establishment.